This invention is directed to a method for reconditioning welded joints of a continuous ferrous strand having a coating thereon comprised of an aluminum-zinc alloy. More particularly, this invention relates to a method of (1) welding aligned, Al-Zn alloy coated ferrous wires, (2) annealing the welded joint, and (3) restoring the corrosion resistant properties to the annealed joint area.
The commercial success of a metallic coated wire, dictated in large measure by ASTM specifications and customer requirements, requires that welded joints of such coated wire be suitably reconditioned to provide (1) atmospheric corrosion resistance substantially equivalent to that of the coated wire, and (2) improved ductility to allow for bending of the coated wire. In addition to the property of improved ductility or flexibility, there are the further desirable product qualities of coating smoothness, appearance and adherence.
The prior art, as represented by the references below, does not teach a method of suitably reconditioning the welded joint of aluminum-zinc alloy coated wire, nor to achieve the desirable coating qualities needed for a commercially viable product.
1. ASTM standard, Designation A780-80, describes a procedure for the repair of damaged hot-dip galvanized coatings. Section Al specifically refers to the use of zinc-based alloys for such repair. The procedure includes the steps of (a) suitably cleaning the area to be reconditioned, which cleaning may comprise mechanical means, such as wire brushing, (b) preheating said area to a temperature in the range of 600.degree. to 750.degree. F. (315.degree. to 400.degree. C.) while wire brushing the surface of the area, (c) rubbing the preheated area with a repair stick to deposit an evenly distributed layer of the zinc-base alloy, and, (d) cleaning the repaired area, such as by the use of water to remove flux residue.
2. U.S. Pat. No. 2,101,816 (McBride) for "Galvanizing Composition" is directed to a flux-metal composition to repair damaged galvanized coatings. The composition, to be applied to the damaged area at a temperature of 500.degree. to 600.degree. F. (260.degree. to 315.degree. C.), comprises an alloy of lead, tin and zinc, admixed with a flux capable of dissolving metal oxide.
3. U.S. Pat. Nos. 2,150,929 and 2,255,979 (Kohler) relate to methods for repairing damaged galvanized coatings. The methods include the step of protecting the damaged areas by amalgamating mercury, alone or with lead, respectively, with the protective zinc coating. No preheating of the damaged areas is required for these repair techniques.
The present invention represents an effective method of reconditioning a welded area in an aluminum-zinc alloy coated product by restoring the corrosion resistant properties thereof, while improving the core properties. The prior art, as exemplified by the above references, fail to provide an effective manner of achieving the dual goals of this invention.